1. Field of the Invention
The present invention relates to a wireless communication device, a wireless communication method, and a wireless communication program, and more particularly, to a technology of performing product detection on a signal received from another wireless communication device by using an arbitrary oscillation frequency, and using a demodulated signal through the product detection.
2. Description of the Related Art
In a communication method (telegraphic communication) in which a continuous wave (CW) is intermittently sent/received as codes, without being limited to amateur wireless communication, a signal whose frequency is close to a transmission frequency (frequency of a received signal) of a counterpart station and generated by a beat frequency oscillator (BFO) is mixed with the transmission frequency, and beats are generated (product detection) so as to make the CW audible. A demodulation frequency is a difference between a reception frequency and an oscillation frequency of the BFO. A pitch frequency denotes a difference between the reception frequency and the oscillation frequency of the BFO in a case where the transmission frequency of the counterpart station and the reception frequency of a self station are equal to each other. The pitch frequency is generally an arbitrary frequency in a 400 to 800 Hz frequency range. Also, since an audible range is different for each person, a pitch frequency is variable according to a user in a high-end wireless device (multi-functional device). When the reception frequency may be set so that the demodulation frequency is a desired pitch frequency, the reception frequency of the self station may be appropriately tuned (zero-in) with respect to the transmission frequency of the counterpart station.
Also, in order to maximize utilizing efficiency of the frequency, it needs to coincide the transmission frequency of the counterpart station with a transmission frequency (and the reception frequency) of the self station. Here, as a method of tuning the reception frequency of the self station to the transmission frequency of the counterpart station, a user mainly performs a manipulation of changing the reception frequency manually so that a tone of the CW demodulated sound can be matched to a side tone (monitoring sound during key-down in order to transmit the CW). By setting a frequency of the side tone to be equal to a pitch frequency, the frequency of the side tone may serve as a reference for the demodulation. That is, when the user performs a manipulation of matching a tone of the CW to a tone of the side tone, the frequency of the CW demodulated sound can match the frequency of the designated pitch frequency, and accordingly, the reception frequency of the self station may be properly tuned to the transmission frequency of the counterpart station.
However, in regard to the above tuning manipulation, the user needs to be skilled. The patent document 1 discloses a wireless device to address this problem.
The wireless device has a receiving circuit, an auto notch filter, a frequency determination processing filter, and a frequency synthesizer. The receiving circuit decodes an input signal to output the decoded signal as a reception signal based on an output frequency from the frequency synthesizer. The auto notch filter performs an adaptation operation, in which a filter coefficient is updated so that a notch frequency is suitable for the reception signal output from the receiving circuit, and outputs the filter coefficient. The frequency determination processing circuit calculates a difference between a notch frequency that is obtained from the filter coefficient output from the auto notch filter and a pitch frequency that is set in advance, and controls an output frequency of the frequency synthesizer so that the above difference becomes zero. As such, tuning of the CW may be performed automatically.
However, according to the wireless device disclosed in the patent document 1, only the automatic tuning has been considered, and there is no consideration of a case where an S/N (signal-to-noise ratio) of the CW is degraded. That is, according to the wireless device disclosed in the patent reference 1, accuracy of the tuning is lowered when the S/N of the CW is degraded. Also, when the CW, the S/N of which is degraded, is demodulated, if a noise reduction for improving the S/N is performed, demodulated sound is also degraded, and thus, suppressed noise becomes unnatural.
3. Prior Art Reference    (Patent Reference 1) Japanese Laid-open Patent Publication No. hei 10-224185